1. Technical Field
The present disclosure relates to ultrasonic electro-mechanical resonant systems. More specifically, the present disclosure relates to improvements in the design and implementation of a feedback system employing the configuration and orientation of coils that enhance the effects of motional or velocity feedback signals and minimize the effects of transformer coupling.
Additionally, the present disclosure relates to a detection system to determine the impedance or inductance of a tool placed in an ultrasonic handpiece. This system includes the ability to differentiate or select tool characteristics prior to and after activation.
2. Background of Related Art
In general, magnetostrictive, electro-mechanical resonant systems are driven by applying an AC signal to a coil that activates a magnetic or ferro-magnetic member, hereinafter referred to as a transducer, by creating a magnet field. The resultant magnetic field creates compressional or standing waves in the transducer, causing it and parts connected thereto to vibrate. The aggregate assembly of the transducer and connected parts, which are hereinafter referred to as tools, are typically supported at nodal points of the longitudinal motion to minimize any loss of motion or kinetic energy of the vibrating tool. The energy created in the vibrating tool may be applied in performing ultrasonic machining, welding, cleaning, dental calculus debridement, or other applications. It is desirable to operate the tool with maximum amplitude of vibration at the working end of the tool. This is achieved when the drive signal is at one of the frequencies of resonance of the transducer or tool.
The desired frequency of resonance is affected by wear, tool geometry, operational temperature, and loading of the tool. To maximize the utility of the tool, the operational frequency of the system drive should be capable of varying in response to the dynamic tool resonance conditions.
Currently produced ultrasonic systems that use some form of feedback to control the drive frequency are limited by a multitude of compromises. The following are some examples of these compromises.
Systems that use the current and voltage characteristics in the drive circuits typically simulate a motional characteristic at a single operating point and use its value for all drive levels.
Most feedback systems that employ a feedback coil near the free end of the transducer to detect the velocity or motion of the transducer use a few turns of reverse drive winding to minimize the transformer coupling effects. This poses several problems. Such reverse winding require the drive levels to be higher than otherwise required because the reverse winding subtracts from the total drive signal. Additionally, the feedback winding needs to be isolated from the end of the drive winding by adding a gap between the windings. Shortening the length of the drive winding limits the total length of the driving magnetic field. The number of turns on the reverse winding is critical because they affect the phase relationship between the drive and feedback signals.
Systems that employ two symmetrical windings wound in reverse magnetic sense are position sensitive, which is in part due to the non-homogeneity of the drive field. These systems are also sensitive to nodal point positioning of transducers with systems using interchangeable tools. This configuration of feedback typically requires some form of post feedback signal conditioning which modifies the phase information, and/or requires the addition of a capacitor across the winding(s).
Some ultrasonic systems provide the option of interchangeable tools. The performance of these tools can vary as a result of certain parameters of the tools. If the impedance varies, for example, corrections could be made to the performance with knowledge of the parametric value. In another instance, a system may have removable tools that provide fundamentally different operations such as ultrasonic vibration and induction heating.
Currently available systems typically use voltage or current levels and frequency or phase information in conjunction with logic circuits that interpret the values. For example, Karnaugh maps or similar Boolean operations are used to select one operational mode or the other. Inherent limitations associated with these prior art systems are that these inputs are often ambiguous due to the effects of manufacturing variations in the tools and operational variations during tool loading.
The present disclosure takes advantage of the non-homogeneous magnetic fields and has been successfully modeled and works without additional signal conditioning. It is the asymmetry of the two coil configuration that makes the difference, with the three coil configuration producing the best results.